The need for access to the circulation is paramount for delivery of renal replacement therapy (RRT) by hemodialysis. The use of a native arterio-venous (AV) fistula provides access with the fewest complications of thrombosis, infection and hospitalization. The creation of the AV fistula is followed by a maturing time in which vascular remodeling occurs. The natural history of this process is not well defined. Moreover, the current challenges of vascular access are expected to increase over time as the typical incident patients are older and have more co-morbid vascular and metabolic disease.